The present invention relates to the field of battery monitoring systems. In particular, the present invention relates to battery monitoring systems that are capable of measuring battery float current levels.
In the telecommunications industry, battery strings are typically used as back-up power sources for telecommunication loads. Telecommunication loads are normally powered by an AC to DC converter. If, however, there is an AC power outage, the battery strings deliver power to the load so that telecommunication services are not interrupted.
To ensure that the battery strings are in sufficient condition to supply power to the load when needed, battery string state-of-health indicators are monitored. One state-of-health indicator that has been found to be particularly useful to monitor is the float current for each battery string. The battery charge/discharge current is typically determined by measuring the voltage across a resistive shunt that is connected in series between the battery string and the load. The present invention provides circuitry capable of measuring the battery float current from the same shunt used to measure the battery charge and discharge currents.
The magnitude of the current flowing through the shunt can vary between large positive and negative readings (charge and discharge respectively) depending on whether the battery is discharging to provide power to the load, recharging after it has provided power to the load, or sitting in a fully charge state with only float currents flowing. A float current may be as small as 0.1% of a battery shunt""s rated current capacity. Because the battery current is generally calculated by measuring the voltage across the shunt and the typical shunt yields 50 mV when the fall rated current is flowing through the shunt and only 50 xcexcV when 0.1% rated current is flowing through the shunt, a measuring device having high precision, accuracy, and resolution is needed to measure the current.
Present systems for measuring float current include hand-held float current measurement devices that are capable of measuring currents only from about 0.01 A to 200 A with a response time of 2 to 7 minutes. These devices are disadvantaged in that their range may not be capable of measuring the larger charge and discharge currents and the smaller float currents, require a human operator to manually take measurements, are not capable of distinguishing a float current from a small charge current, and consequently require a human operator to manually enter data if trends are to be monitored.
Other systems for measuring float current include Hall effect devices. The major shortcoming of Hall effect devices is offset error. Hall effect devices sized to read the charge and discharge current levels are not capable of reading the float current at all due to the 1-2% offset error which makes the float current reading undetectable. Hall effect devices sized to read the float current level saturate at the larger charge and discharge current levels, which makes the charge and discharge readings undetectable. As a result, the Hall effect device has insufficient resolution for this application.
Closed loop Hall effect with proper supporting circuitry are capable of reading the charge, discharge and float currents but are cost prohibitive at this time.
Present systems are not capable of distinguishing a float current reading from a small charge current.
Therefore, there remains a need for a float current monitoring system that has the precision, accuracy and resolution to measure battery float current as well as discharge and charge currents. There remains a particular need for a float current monitoring system that is capable of making the measurements without human intervention possessing the capability to distinguish a float current from a small charge current and record historical data.
The present invention meets the foregoing needs by providing a battery monitoring system for monitoring the state-of-health of batteries in a power distribution system. The preferred system is capable of measuring battery currents ranging from full charge to full discharge with a resolution capable of reading float current levels. The preferred system includes a software algorithm that determines when the battery string is drawing a float charge. When the preferred system determines that it is measuring float current, the preferred system is capable of providing a notification via visual, audible, or remote reporting that float currents are out specification in accordance with user configured alarm thresholds. The preferred system is also capable of recording historical data for use in calculating daily, weekly, or monthly float current averages.
The present invention provides many advantages over the presently known float current monitoring systems. Not all of these advantages are simultaneously required to practice the invention as claimed, and the following list is merely illustrative of the types of benefits that may be provided, alone or in combination, by the present invention. These advantages include: (1) the system""s automatic operation; (2) the lack of a need for a human operator to take measurements; and (3) the systems flexibility in being easily configurable to take measurements from shunts having different capacities.
In accordance with one aspect of the present invention, a battery monitoring system is provided that comprises a field measurement device and a monitor. The field measurement device is located in close proximity to a battery to be monitored. The field measurement device includes an input mechanism for receiving current measurement data and an analog-to-digital converter for digitizing the received current measurement data. The monitor is located remotely from the field measurement device. The monitor includes a communicator for receiving digitized data from the field measurement device.
In accordance with another aspect of the present invention, a power distribution system is provided comprising a power regulator, a battery circuit, and a battery monitoring system. The power regulator is provided for converting AC power to DC power and for providing DC power to a load. The battery circuit is coupled to the power regulator and the load and is operable to recharge by receiving DC power from the power regulator. The battery circuit is also operable to supply DC power to the load when there is an interruption of power from the load. The battery monitoring system comprises a field measurement device located in close proximity to the battery circuit, the field measurement device including an input mechanism for receiving current measurement data and an analog-to-digital converter for digitizing the received current measurement data. The battery monitoring system further comprises a monitor located remotely from the field measurement device, the monitor including a first communicator for receiving digitized data from the field measurement device.
In accordance with another aspect of the present invention, a battery monitor for use in a power distribution system is provided. The battery monitor comprises a monitor CPU for monitoring the state of health of a battery in the power distribution system and a shunt interface circuit having a first communicator and a shunt interface controller, the first communicator being operable to communicate with a field measurement device located in close proximity to the battery, the field measurement device being operable to communicate state-of-health information regarding the battery, and the shunt interface controller being operable to communicate the state-of-health information to the monitor CPU.
In accordance with another aspect of the present invention, a field measurement device for use in a power distribution system is provided. The field measurement device comprises an input mechanism for measuring battery state-of-health information regarding a battery, an analog-to-digital converter for digitizing the measured battery state-of-health information, and a communicator for communicating the digitized battery state-of-health information to a remotely located battery monitor.
In accordance with another aspect of the present invention, a method for remotely monitoring the state-of-health of a plurality of batteries in a power distribution system is provided. The method comprises the steps of providing a plurality of plurality of field measurement devices, each device being in close proximity to one of the batteries, performing a battery state-of-health measurement on at least one of the batteries, communicating the battery state-of-health information to a monitoring system; and displaying information regarding the state-of-health of the battery at the monitoring system.